1. Field of the Invention
This invention is directed to a sub-miniature optical fiber cable, and to apparatuses and methods for making the sub-miniature optical fiber cable.
2. Description of the Related Art
Local exchange carriers are increasingly using optical fiber signal transmission in central offices to accommodate the increasing demand for optical fiber systems such as fiber-to-the-home, fiber-to-the-curb, hybrid fiber-coax, digital loop carrier and interoffice carrier systems. The central offices are used to distribute optical fiber cables and to establish cross-connections between optical fiber systems and/or exchanges. At present, optical fiber cable is produced in standard sizes of 2.4 mm or 3 mm in diameter. Although these standard sizes may appear to be relatively small in diameter, because they are used in such large numbers in a central office, these standard sizes lead to significant congestion, complication and expense in a central office. In fact, to accommodate cross-connections between optical fiber systems or exchanges, central offices require a relatively large number of cabinets with troughs housing optical fiber jumper cables, and racks housing connectors to join optical fiber jumper cables together. The relatively large number of cabinets currently required in a central office to accommodate cross-connections for optical fibers increases the size and space requirements for central offices and thus the expense of the central offices. Moreover, the relatively large standard sizes of optical fiber cables lead to congestion and complication in the central office which requires significant time, and therefore expense, for service persons to establish, replace, change or maintain cross-connections in the central offices. Further, the size of the optical fiber cable has a multiplicative effect on the size of the components that are used with the cable in the central office. Thus, if the optical fiber cable is relatively large, so must be the connectors which terminate and attach the optical fiber cable to other optical fiber cables, the size of the racks that house the connector receptacles, the troughs which house the optical fiber jumper cables, and the size of the cabinets used to house the racks and troughs. If the size of the optical fiber cables can be reduced, the connectors, racks, troughs and cabinets can be proportionally decreased in size.
Also noteworthy is that the cost of the optical fiber cables, connectors and cabinets is proportional to the amount of materials used in the manufacture thereof. Therefore, by decreasing the size of the optical fiber cables, connectors and cables, significant cost-savings can be obtained. Thus, there is a need to reduce the size of optical fiber cables.
This invention overcomes the disadvantages noted above. In accordance with this invention, a simplex optical fiber cable includes a jacketed optical fiber at its core. The optical fiber is surrounded and contacted with a buffer made of plastic material such as nylon, polyesters or polyvinyl chloride (PVC). About the outer circumference of the buffer, aramid yarn is disposed. A sheath of plastic material such as PVC surrounds and contacts the aramid yarn.
A duplex optical fiber cable in accordance with this invention includes two optical fibers with respective buffers and aramid yarn layers, which are positioned side-by-side in a sheath, preferably of PVC, covering and contacting the aramid yarn of both optical fibers and integrated together to form a continuous connection between portions of the sheath covering respective aramid yarn layers, buffers and optical fibers. In an alternative embodiment, a duplex optical fiber cable in accordance with this invention includes two simplex optical fiber cables as previously described, positioned side-by-side and having an oversheath, preferably of PVC, enclosing the two simplex optical fiber cables.
In cross-section, the diameter of the simplex optical fiber cable can range from 1.0 mm through 1.8 mm, but is preferably formed in standard sizes of about 1.2 mm and 1.6 mm. The simplex optical fiber cable of this invention is thus significantly smaller in diameter than the optical fiber cables presently available. Likewise, in cross-section, the duplex optical fiber cable of this invention ranges from 2.76 mm through 4.25 mm in width and from 1.60 mm through 2.10 mm in height, but preferably is formed in standard sizes of about 2.76 mm in width and 1.68 mm in height, or about 4.20 mm in width and 1.60 mm in height. Thus, the duplex optical fiber cable of this invention is much smaller in cross-section compared to duplex optical fiber cables presently available.
Thus, the simplex and duplex optical fiber cables of this invention are miniaturized relative to prior art optical fiber cables, and make possible the reduction of congestion, complication and size and space requirements presently required in central offices. These features of the simplex and duplex optical fiber cables of this invention considerably reduce the costs of establishing, operating and maintaining central offices.
In accordance with this invention, if the buffer surrounding the optical fiber is relatively thin in either the simplex or duplex cable configuration, a slick substance such as talc can be applied to the outer surface of the buffer. This feature of this invention allows for the buffer to slide in contact with its aramid yarn layer so that the optical fiber will not be overbent when the ferrule of a connector attached to an end of the optical fiber, forces the optical fiber in an axial direction along the length of the optical fiber cable as the connector is connected to a connector receptacle. Thus, the simplex and duplex optical fiber cables of this invention reduce damage or breakage of optical fibers caused by overbending or fatigue when a connector is coupled to a connector receptacle.
Also, in either the simplex or duplex cable configurations, if the buffer is relatively thick, a slick substance such as MODAFLOW(copyright) can be applied to the outer surface of a coated optical fiber so that the relatively thick buffer can more readily be stripped from the optical fiber.
In addition, the duplex optical fiber cables of this invention are advantageous in that the respective buffers of the two optical fibers in each duplex optical fiber cable of this invention are individually wrapped with aramid yarn as opposed to wrapping aramid yarn around the buffers of both optical fibers as done in one type of optical fiber cable presently available. By individually wrapping the two optical fiber buffers in the duplex optical fiber cable of this invention, the need for bifurcation kits to connect the duplex optical fiber cable to single connectors, is eliminated. Because bifurcation kits have parts which force the diameter of the optical fiber cable to increase greatly, the elimination of the need for bifurcation kits effectively reduces the size of the duplex optical fiber cable of this invention relative to presently available duplex optical fiber cables. Also, bifurcation kits are relatively expensive, so the elimination of the need to use bifurcation kits in the duplex optical fiber cables of this invention provides significant cost-savings relative to duplex optical fiber cables which require bifurcation kits.
The invention further includes die assemblies and methods for making the simplex and duplex optical fiber cables of this invention. The die assemblies have several component parts which can easily be replaced if damaged, thus saving the cost of having to replace an entire die as required in the prior art. The die assemblies further split flows of molten plastic material and have surfaces which cause the split flows to converge to increase uniformity of the sheath or oversheath of the simplex or duplex optical fiber cable.
These together with other objects and advantages, which will become subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings, forming a part hereof, wherein like numerals refer to like parts throughout.